1. Field of the Invention
This invention relates to forming iron phosphate conversion coatings, with substantially higher coating weights than are normal for iron phosphating, on ferriferous substrates, to compositions suitable for forming such coatings by contact with ferriferous metal substrates, and to use of the coatings formed as a carrier for lubricants during drawing and/or other forms of cold working of the coated substrates.
2. Discussion of Related Art
Iron phosphating is well established as a pre-painting treatment. For this purpose, phosphating compositions with a pH value higher than 3.8 are generally used, and the coating weights of the phosphate coatings formed are generally from 0.3 to 1.5 grams per square meter (hereinafter usually abbreviated as "g/m.sup.2 "). Phosphating is also well established as a process for forming a base surface on which to apply a lubricant, conventionally a soap such as zinc and/or sodium stearate, to prevent mechanical damage during cold working, especially tube drawing. For this purpose, however, much heavier coating weights of at least 2 g/m.sup.2 and normally 6-9 g/m.sup.2 are usually used. In the past, such coating weights have normally been achieved by using zinc containing phosphating compositions. Zinc phosphating compositions are highly effective for this purpose, but zinc and other "heavy" metals such as nickel and manganese that are often contained in zinc phosphating compositions are being increasingly regarded as pollutants, so that their elimination would be advantageous, if adequate lubricant carrier conversion coatings could be produced without them.